Theoretical and empirical models that aim at explaining the patterns of legislative decision-making in parliamentary democracies focus on the policy preferences of political actors and institutional constraints. In doing so, incentives of MPs originating from their personal traits to take a particular position are often ignored. In this paper, we argue that personal characteristics and experiences like the religious denomination shape MPs’ preferences, and that they should therefore play a decisive role for the behavior of MPs in legislative decision-making processes. However, given parties strength in most parliamentary systems, the latter typically only holds when it comes to parliamentary votes on issues related to moral or religious aspects. We select the German Bundestag as an example for generally highly disciplined MPs and a high degree of parliamentary party unity. Our analyses of the parliamentary debate and votes on the regulation of preimplantation genetic diagnosis (PGD) show that the legislative behavior of MPs is not only influenced by partisan issues and the preferences of the MPs respective constituency, but also by MPs personal traits like religious denomination, gender and parental status.